A rotary electric machine such as an alternator, generator or an electric motor (generator) in a vehicle produces heat. Various air cooling systems have been used in the past to prevent overheating of the machine. However, the cooling capacity of such a system may not be sufficient to produce the desired cooling effect. This limitation can constrain the output current from the alternator.
To increase cooling efficiency, a cooling system utilizing water as a coolant has been proposed. For example, U.S. Pat. No. 5,655,485 discloses a rotary electric machine having an engine-cooling water pump integrally combined therewith and disposed next to the stator of the engine. The disclosed water pump and the alternator have the same drive shaft, which is driven by the crank shaft of the engine. The impeller of the water pump is rotated at the same speed as the rotor and drives water through the water passage to cool the stator.
The inventor herein has recognized several disadvantages of the above approach. For example, coolant flow rate cannot be adjusted independently to control the engine and the alternator temperature based on the engine operating conditions. Further, the location of the water pump increases the length of the alternator assembly, which can be undesirable from a packaging perspective.
To address the above problems, an integrated alternator and water pump for a vehicle is provided. The integrated alternator and water pump comprises an alternator rotor mounted on a first drive shaft; and a water pump impeller mounted on a second drive shaft, wherein the water pump impeller is configured to cause pumping of coolant in response to rotation of the second drive shaft, and where the first and second drive shafts are operatively coupled such that rotation of the first drive shaft imparts rotation to the second drive shaft. In one embodiment, the speed of the water pump impeller can be varied different from the alternator rotor. Thus, coolant flow rate can be adjusted in response to an engine operating condition such as an engine temperature.
According to another aspect, an integrated alternator and water pump for a vehicle are provided. The integrated alternator and water pump comprises an alternator rotor mounted on a first drive shaft; and a water pump impeller mounted on a second drive shaft, wherein the water pump impeller is configured to cause pumping of coolant in response to rotation of the second drive shaft, and where the first and second drive shafts are operatively coupled such that rotation of the first drive shaft imparts rotation to the second drive shaft. In one embodiment, drive shafts of the alternator and water pump are not coaxial. Thus, the water pump can be disposed at the top, bottom and sides of the alternator. These configurations can reduce the packaging limitations of the alternator.
According to yet another aspect, a method of controlling alternator temperature and engine temperature for a vehicle is provided. The method comprises rotating a first drive shaft to generate electricity during operation of an engine; rotating a second drive shaft to cause pumping of coolant to cool at least portion of the alternator and the engine where the first and second drive shafts are operatively coupled such that rotation of the first drive shaft imparts rotation to the second drive shaft; and selectively routing coolant through multiple different fluid pathways in response to an engine operation condition.
In one embodiment, coolant is routed through the alternator and the engine without routing through a heat exchanging device when the engine temperature is low. In this way, the heat generated from the alternator can be used to warm up the engine coolant during cold start because the alternator coils and electronics heat faster than the engine. Thus, the time for the engine to reach the efficient operating temperature can be reduced. Consequently, fuel economy and emission reduction can be improved.